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10th April 2019, Stamford, CT

High-volume, zero-waste process with Hexcel moulding compound

The preform. © Hexcel

The preform. © Hexcel

A high-performance moulding compound from Hexcel has been used to produce a carbon fibre-reinforced plastic (CFRP) transmission crossmember using a zero-waste process ideal for high-volume manufacture. The automotive part is comparable with aluminium versions in terms of its performance and price, but could be 30-35% lighter.

The transmission crossmember has been developed by Hexcel, Engel, Alpex and the Institute of Polymer Product Engineering (IPPE) at the University of Linz.

“These parts connect either side of a vehicle’s chassis together and support its transmission, and must be stiff, strong, and resistant to fatigue,” explains Hexcel’s Director of Sales and Marketing for Automotive, Achim Fischereder. “As they are exposed to the road, they must also be resistant to stone chipping and corrosion caused by water and salts.”

To meet these requirements, the partners selected HexMC-i 2000, which is the best-performing moulding compound currently on the market, to produce the part. HexMC-i 2000 has been designed specifically to bridge the price-performance gap between sheet-moulding compounds (SMCs) and prepregs, and is stiffer than steel at approximately a fifth of the density. Further, its mechanical performance is highly consistent.

Preforms of HexMC-i 2000 are laid up in moulds fabricated by Alpex and compression-moulded using an Engel v-duo press. © Hexcel

Preforms of HexMC-i 2000 are laid up in moulds fabricated by Alpex and compression-moulded using an Engel v-duo press. © Hexcel

HexMC-i 2000 comprises randomly-orientated rectangular chips of unidirectional carbon fibre-reinforced prepreg impregnated with Hexcel’s M77 snap-curing epoxy resin to form a 2,000gsm sheet material. The moulding compound can cure in as little as two minutes to produce lightweight, strong and stiff parts.

To produce the transmission crossmember, preforms of HexMC-i 2000 are laid up in moulds fabricated by Alpex and compression-moulded using a v-duo press that has been tailored for the application from Engel. Ribs, aluminium inserts and other functions can be moulded into the part using the single-stage process, reducing component-count in comparison with metal versions of the part and keeping costs low. 

Crucially, any offcuts from the preforms can be interleaved between the plies of material to provide additional reinforcement in key areas, meaning that the process generates no waste whatsoever.

Another option being explored by the partners is to transform these offcuts into carbon fibre mat prepreg using techniques developed by Carbon Conversions Inc. (CCI), a company in which Hexcel acquired a stake in late 2016.

The finished part. © Hexcel

The finished part. © Hexcel

Thanks to advanced finite element method (FEM) simulation techniques developed by IPPE, the design of the part is highly optimised, and it demonstrates the strength and fatigue-resistance demanded by the application.

“Hexcel is looking forward to working with our partners to further harness the benefits of high-performance HexMC-i 2000,” Achim Fischereder concludes. “Using the predictable, zero-waste process we have developed, we have shown that we can match the performance and price of metallic structural components while reducing weight significantly.”

The full case study can be viewed here.

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